The proposed International Study of Schizophrenia is designed to extend the progress achieved in the IPSS (International Pilot Study of Schizophrenia) by further developing simple and reliable methods for the identification and assessment of psychiatric patients, particularly those suffering from schizophrenia, in different sociocultural settings. It also aims at the development of suitable techniques for the study of the course of schizophrenia and other mental diseases and their natural history and outcome under different socio-economic and cultural conditions. The 1,200 patients included in the study in the nine countries are being followed up over a period of five years and data obtained about the cohorts of patients who were assessed and followed up in a standardized way in each centre will serve as the basic material for comparative studies of the influence of sociocultural factors on the course and outcome of psychiatric disorders, and of psychopathology of schizophrenia and other mental disorders. Methods and procedures developed in the study would also be used for intensive studies of social, cultural, psychological and other factors which may cause, precipitate, exacerbate or prevent schizophrenia and other mental disorders. Another important aim of the ISS is the development and further strengthening of a network of research and training centres in different parts of the world. In addition to their work in this study these centres have already become engaged in a number of additional studies. It is expected that they will serve as a basis for further studies in crosscultural and epidemiological psychiatry.